1. Field of the Invention
The present invention relates to a pick-up for measuring the velocity of a gas based on an ionization phenomenon and, more particularly, to a pick-up for measuring the air supply speed at the cylinder intake of an internal combustion engine by ion transit time.
2. Description of the Prior Art
French patent application No. 78/29.884, filed by the applicant on Oct. 20, 1978, for a "Device for measuring the fill volume of air in a motor", remarkable relative to measuring the quantity of air R necessary to fill the cylinders of an internal combustion engine, is known, and such device uses, in combination:
a mechanism for measuring the air flow velocity inside an inlet manifold which is an anemometer of the transit time, having two electrodes, associated with a high tension impulse generator;
a mechanism for releasing the impulse generator (triggger) attached at an angular position of the main shaft and a mechanism for complex calculation, incorporating specifically a micro-calculator which makes it possible to carry out the measurement or the target (privileged) times to obtain the quantity R.
Thus, a pick-up for measuring the velocity of gas and, specifically, of air in which a first electrode ionizes the gas and one or more other electrodes, receptacles, gathers a portion of the ions with a delay proportional to the distance and the velocity.
If one wants to use the device for the air admitted at the intake of an internal combustion engine with an air valve, there are certain problems in obtaining a very precise device because the total length arrangement of the measurement base and the response velocity is not always easy to optimize, particularly when there is rapid intake valve movement. When the motor turns very rapidly, and when intake is finished at a position corresponding to the idle speed setting, very little air continues to enter the motor, which signifies a weak velocity in the measuring organ in front of the valve.
The same problem may occur in measurements of other than internal combustion engines if there is a large velocity pressure and when it is controlled by a valve.